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Biomedical subjects

R E Gregg

Publications and source records attributed to R E Gregg.

At least 37 records · Page 2Linked to original sources
PubMed1995

Microsomal triglyceride transfer protein: a protein complex required for the assembly of lipoprotein particles.

The mechanism of assembly of lipoprotein particles in the lumen of the endoplasmic reticulum is an important but poorly understood biological problem. A knowledge of this process is of great practical importance because possession of elevated levels of lipoproteins is one of the major risk factors for the development of atherosclerosis. This review describes a major advance in the delineation of the mechanisms involved in the assembly and secretion of apolipoprotein-B-containing lipoproteins: the demonstration of a requirement for microsomal triglyceride transfer protein.

Journal Article↗
PubMed1995

Dominant expression of type III hyperlipoproteinemia. Pathophysiological insights derived from the structural and kinetic characteristics of ApoE-1 (Lys146-->Glu).

Type III hyperlipoproteinemia is characterized by delayed chylomicron and VLDL remnant catabolism and is associated with homozygosity for the apoE-2 allele. We have identified a kindred in which heterozygosity for an apoE mutant, apoE-1 (Lys146-->Glu), is dominantly associated with the expression of type III hyperlipoproteinemia. DNA sequence analysis of the mutant apoE gene revealed a single-point mutation that resulted in the substitution of glutamic acid (GAG) for lysine (AAG) at residue 146 in the proposed receptor-binding domain of apoE. The pathophysiological effect of this mutation was investigated in vivo by kinetic studies in the patient and six normal subjects, and in vitro by binding studies of apoE-1 (Lys146-->Glu) to LDL receptors on human fibroblasts and to heparin. The kinetic studies revealed that apoE-1 (Lys146-->Glu) was catabolized significantly slower than apoE-3 in normals (P < 0.005). In the proband, the plasma residence times of both apoEs were substantially longer and the production rate of total apoE was about two times higher than in the control subjects. ApoE-1 (Lys146-->Glu) was defective in interacting with LDL receptors, and its ability to displace LDL in an in vitro assay was reduced to 7.7% compared with apoE-3. The affinity of apoE-1 (Lys146-->Glu) to heparin was also markedly reduced compared with both apoE-2 (Arg158-->Cys) and apoE-3. These abnormal in vitro binding characteristics and the altered in vivo metabolism of apoE-1 (Lys146-->Glu) are proposed to result in the functional dominance of this mutation in the affected kindred.

Adult↗
PubMed1994

Secretion of apolipoprotein B-containing lipoproteins from HeLa cells is dependent on expression of the microsomal triglyceride transfer protein and is regulated by lipid availability.

To elucidate the role of the microsomal triglyceride transfer protein (MTP) in lipoprotein assembly, MTP and apolipoprotein B-53 (apoB 53; the N-terminal 53% of apoB) were expressed in HeLa cells. The results showed that apoB-53 could be expressed in HeLa cells with or without expression of MTP. In contrast, efficient secretion of apoB-53 required expression of MTP. Ultracentrifugal density flotation analysis showed that apoB-53 was secreted predominantly as a particle with the density of high density lipoprotein. An essentially identical apoB-53 particle density distribution was obtained after transient expression of apoB-53 in McArdle RH-7777 rat hepatoma cells. The mass of apoB-53 secreted was greater, and the flotation density was lower, from cells fed lipid, suggesting that apoB secretion in HeLa cells was regulated by lipid availability, similar to what has been described for lipoprotein-producing cell lines. These results indicate that MTP is necessary and sufficient to direct the regulated secretion of apoB-53 in HeLa cells.

Animals↗
PubMed1994

The molecular basis of abetalipoproteinemia.

Abetalipoproteinemia is a recessive genetic disease in humans characterized by the virtual absence of apolipoprotein (apo)B and apoB-containing lipoproteins in plasma. Microsomal triglyceride transfer protein (MTP), a resident lipid transfer protein within the endoplasmic reticulum of hepatocytes and enterocytes, has been shown to be absent in enterocytes from subjects with this disease. MTP is a heterodimer of a unique large subunit and protein disulfide isomerase. It has been demonstrated that the absence of MTP in abetalipoproteinemia is secondary to mutations in the gene for the large subunit of MTP. Thus, mutations in the gene for the large subunit of MTP are a cause of abetalipoproteinemia, which indicates that the MTP is a necessary component for the assembly and secretion of apoB-containing lipoproteins from the liver and intestine.

Abetalipoproteinemia↗
PubMed1993

In vivo metabolism of a mutant form of apolipoprotein A-I, apo A-IMilano, associated with familial hypoalphalipoproteinemia.

Apo A-IMilano is a mutant form of apo A-I in which cysteine is substituted for arginine at amino acid 173. Subjects with apo A-IMilano are characterized by having low levels of plasma HDL cholesterol and apo A-I. To determine the kinetic etiology of the decreased plasma levels of the apo A-I in these individuals, normal and mutant apo A-I were isolated, radiolabeled with either 125I or 131I, and both types of apo A-I were simultaneously injected into two normal control subjects and two subjects heterozygous for apo A-IMilano. In the normal subjects, apo A-IMilano was catabolized more rapidly than the normal apo A-I (mean residence times of 5.11 d for normal apo A-I vs. 3.91 d for apo A-IMilano), clearly establishing that apo A-IMilano is kinetically abnormal and that it has a shortened residence time in plasma. In the two apo A-IMilano subjects, both types of apo A-I were catabolized more rapidly than normal (residence times ranging from 2.63 to 3.70 d) with normal total apo A-I production rates (mean of 10.3 vs. 10.4 mg/kg per d in the normal subjects). Therefore, in the subjects with apo A-IMilano, the decreased apo A-I levels are caused by rapid catabolism of apo A-I and not to a decreased production rate, and the abnormal apo A-IMilano leads to the rapid catabolism of both the normal and mutant forms of apo A-I in the affected subjects.

Adult↗
PubMed1992

Absence of microsomal triglyceride transfer protein in individuals with abetalipoproteinemia.

Abetalipoproteinemia is a human genetic disease that is characterized by a defect in the assembly or secretion of plasma very low density lipoproteins and chylomicrons. The microsomal triglyceride transfer protein (MTP), which is located in the lumen of microsomes isolated from the liver and intestine, has been proposed to function in lipoprotein assembly. MTP activity and the 88-kilodalton component of MTP were present in intestinal biopsy samples from eight control individuals but were absent in four abetalipoproteinemic subjects. This finding suggests that a defect in MTP is the basis for abetalipoproteinemia and that MTP is indeed required for lipoprotein assembly.

Abetalipoproteinemia↗
PubMed1992

In vivo metabolism of apolipoprotein A-I in a patient with homozygous familial hypercholesterolemia.

Familial hypercholesterolemia (FH), caused by a defect in the low density lipoprotein (LDL) receptor, results in high plasma concentrations of LDL cholesterol due to both overproduction and delayed catabolism of LDL. FH is also associated with significantly lower levels of plasma high density lipoprotein cholesterol and apolipoprotein (apo) A-I in both heterozygous and homozygous patients. However, the metabolic basis of the hypoalphalipoproteinemia in FH has not been elucidated. We investigated the kinetics of apo A-I in a homozygous FH patient and two normal control subjects by using endogenous labeling with a stable isotopically labeled amino acid. Study subjects were administered a primed constant infusion of 13C6-phenylalanine for 12 hours. Apolipoproteins were isolated from plasma drawn at selected time points and analyzed for their isotopic enrichment by gas chromatography-mass spectrometry. The fractional catabolic rate of apo A-I in the FH subject was found to be substantially increased (0.38 day-1) compared with that of the normal subjects (mean, 0.26 day-1). In addition, the apo A-I production rate was decreased in the FH subject (6.5 mg/kg.day-1) compared with the normal subjects (mean, 11.1 mg/kg.day-1). In conclusion, the low levels of high density lipoprotein cholesterol and apo A-I in this homozygous FH patient are due to the combined metabolic defects of increased apo A-I catabolism and decreased apo A-I production.

Apolipoprotein A-I↗
PubMed1992

Clinical, pathologic, and biochemical features of a cholesterol lipidosis accompanied by hyperlipidemia and xanthomas.

We describe the unique clinical and histopathologic features of a child with biochemical and immunocytochemical features of Niemann-Pick disease type C (NPC). Clinically, she was found to have multiple xanthomas of the upper aerodigestive tract with dysphagia and expressive language delay, splenomegaly, bony infarcts, and type IIb hyperlipidemia. Neurologic examination was otherwise normal. Microscopy revealed foam cells in her bone marrow, liver, tongue, tonsils, glottis, and in normal-appearing peritonsillar mucosa. Lipid analysis of a liver biopsy specimen showed a small increase in phospholipids, a twofold increase in sphingomyelin, a fivefold increase in cholesterol, and a marked (25-fold) increase in bis(monoacylglycerol) phosphate. Lysosomal acid hydrolase activities in cultured skin fibroblasts were nondiagnostic. Biochemical and immunocytochemical studies of cultured fibroblasts demonstrated lysosomal accumulation of unesterified LDL-derived cholesterol as well as delayed induction of homeostatic responses to endogenous cholesterol consistent with a diagnosis of NPC. Based upon these observations, we speculate that this patient could have a new phenotypic expression of NPC or represents a new cholesterol lipidosis biochemically resembling NPC. The chance occurrence of two separate lipid disorders seems less likely.

Biopsy↗
PubMed1992

Inhibition of fatty acid synthesis decreases very low density lipoprotein secretion in the hamster.

The hamster was developed as a model to study very low density lipoprotein (VLDL) metabolism, since, as is the case in humans, the hamster liver was found to synthesize apoB-100 and not apoB-48. The effect of inhibiting fatty acid synthesis on the hepatic secretion of VLDL triglyceride (TG) and apolipoprotein (apo) B-100 in this model was then investigated. In an in vivo study, hamsters were fed a chow diet containing 0.15% TOFA (5-tetradecyloxy-2-furancarboxylic acid), an inhibitor of acetyl-CoA carboxylase. After 6 days of treatment, plasma triglyceride and cholesterol levels were decreased by 30.2% and 11.6%, respectively. When the secretion of VLDL-TG by the liver was measured in vivo after injection of Triton WR 1339, TOFA treatment was found to decrease VLDL-TG secretion by 40%. In subsequent in vitro studies utilizing cultured primary hamster hepatocytes, incubation with 20 microM TOFA for 4 h resulted in 98% and 76% inhibition in fatty acid and triglyceride synthesis, respectively; VLDL-TG secretion was decreased by 90%. When hepatocytes were pulsed with [3H]leucine, incubation with TOFA resulted in a 50% decrease in the incorporation of radiolabel into secreted VLDL apoB-100. The results of this study indicate that inhibition of intracellular triglyceride synthesis decreases the secretion of VLDL-TG and apoB-100, and does not result in the secretion of a dense, triglyceride-depleted lipoprotein.

Animals↗
PubMed1992

In vivo metabolism of a mutant apolipoprotein, apoA-IIowa, associated with hypoalphalipoproteinemia and hereditary systemic amyloidosis.

Apolipoprotein (apo) A-I is the major protein constituent of plasma high density lipoproteins (HDL). A kindred has been identified in which a glycine to arginine mutation at residue 26 in apoA-I is associated with hypoalphalipoproteinemia and hereditary systemic amyloidosis. We isolated the mutant protein, termed apoA-IIowa, from the plasma of an affected subject and studied its in vivo metabolism compared to that of normal apoA-I in two heterozygous apoA-IIowa subjects and two normal controls. Normal and mutant apoA-I were radioiodinated with 131I and 125I, respectively, reassociated with autologous plasma lipoproteins, and simultaneously injected into all subjects. Kinetic analysis of the plasma radioactivity curves demonstrated that the mutant apoA-IIowa was rapidly cleared from plasma (mean fractional catabolic rate [FCR] 0.559 day-1) compared with normal apoA-I (mean FCR 0.244 day-1) in all four subjects. The FCR of normal apoA-I was also substantially faster in the heterozygous apoA-IIowa subjects (mean FCR 0.281 days-1) than in the normal controls (mean FCR 0.203 days-1). Despite the rapid removal from plasma of apoA-IIowa, the cumulative urinary excretion of its associated radioactivity after 2 weeks (44%) of the injected dose) was substantially less than that associated with normal apoA-I (78% of injected dose), indicating extravascular sequestration of radiolabeled apoA-IIowa.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Ultrasound guidance of laser atherectomy.

Intravascular ultrasound imaging catheters and forward firing laser atherectomy systems are both being used in the coronary vascular tree of man. When used in conjunction, ultrasound imaging may reduce the probability of perforation and dissection related to laser atherectomy. A novel system is presented which combines ultrasound imaging and laser atherectomy capabilities on the same catheter. The system incorporates a holmium YAG laser directed perpendicular to the long axis of the catheter along with a co-directional ultrasound sensor. Ultrasound images are assembled by computer using the angle of the catheter tip and its linear advance associated with each ultrasound echo signal. In vivo experimental results are presented.

Angioplasty, Laser↗
PubMed1991

Severe hyperlipidemia due to multiple factors in a child with nephrotic syndrome.

An unusual case of severe hypercholesterolemia and hypertriglyceridemia is described in a child with nephrotic syndrome. The severe hyperlipidemia in this patient was most likely induced by multiple interacting factors which included the metabolic abnormalities of nephrotic syndrome, steroid therapy, the underlying genetic predisposition of ApoE-2 homozygosity as well as diet and diuretic therapy. The result of these factors was an extremely severe type III hyperlipoproteinemia. The pathogenesis of hyperlipidemia in this setting is discussed.

Apolipoproteins E↗
PubMed1991

Isolation and characterization of an apoA-II-containing lipoprotein (LP-A-II:B complex) from plasma very low density lipoproteins of patients with Tangier disease and type V hyperlipoproteinemia.

Previous studies have shown that very low density lipoproteins (VLDL) from patients with Tangier disease are less effective as a substrate for human milk lipoprotein lipase (LPL) than VLDL from normal controls as assessed by measuring the first order rate constant (k1) of triglyceride hydrolysis. Tangier VLDL also has a higher content of apolipoprotein (apo) A-II than normal VLDL. To explore the possible relationship between the relatively high concentration of apoA-II in VLDL and low k1 values, Tangier VLDL were fractionated on an anti-apoA-II immunosorber. The retained fraction contained a newly identified triglyceride-rich lipoprotein characterized by the presence of apolipoproteins A-II, B, C-I, C-II, C-III, D, and E (LP-A-II:B:C:D:E or LP-A-II:B complex), whereas the unretained fraction consisted of previously identified triglyceride-rich apoB-containing lipoproteins free of apoA-II. In VLDL from patients with Tangier disease or type V hyperlipoproteinemia, the LP-A-II:B complex accounted for 70-90% and 25-70% of the total apoB content, respectively. The LP-A-II:B complexes had similar lipid and apolipoprotein composition; they were poor substrates for LPL as indicated by their low k1 values (0.014-0.016 min-1). In contrast, the apoA-II-free lipoproteins present in unretained fractions were effective substrates for LPL with k1 values equal to or greater than 0.0313 min-1. These results indicate that triglyceride-rich lipoproteins consist of several apoB-containing lipoproteins, including the LP-A-II:B complex, and that lipoprotein particles of similar size and density but distinct apolipoprotein composition also possess distinct metabolic properties.

Adult↗
PubMed1991

Modified immunoblotting technique for phenotyping lipoprotein(a).

We describe a modified immunoblotting method for phenotyping lipoprotein(a) [Lp(a)]. This immunoblotting procedure uses commercially available reagents that have a long shelf life. The method is sensitive and takes only 18 microL of sera. Lp(a) phenotyping can be performed on sera stored at 4 degrees C for as much as a week or at -80 degrees C for as long as a year. In a study of 145 unrelated healthy subjects, we found Lp(a) allelic frequencies of LpF = 1.8%, LpB = 2.6%, LpS1 = 5.1%, LpS2 = 14.8%, LpS3 = 35.9%, LpS4 = 11.6%, and LpO = 28.0%.

Alleles↗
PubMed1990

A mutation in apolipoprotein A-I in the Iowa type of familial amyloidotic polyneuropathy.

Immunoblotting of isoelectric focusing gels of plasma and direct genomic DNA sequencing have been used to characterize a mutation in apolipoprotein A-I associated with the familial amyloidotic polyneuropathy originally described by Van Allen in an Iowa kindred. An arginine for glycine substitution in apolipoprotein A-I identified in the proband's amyloid fibrils was determined to be the result of a mutation of guanine to cytosine in the apolipoprotein A-I gene at the position corresponding to the first base of codon 26. Direct sequencing of genomic DNA of three affected individuals who died in the 1960s confirmed the inheritance of the disorder. Immunoblot analysis detected the variant apolipoprotein A-I in the proband's plasma and in several at-risk members of the kindred. In addition, allele-specific amplification by the polymerase chain reaction was used to detect carriers of the variant gene.

Amyloidosis↗
PubMed1990

Apolipoprotein A-I metabolism in subjects with a PstI restriction fragment length polymorphism of the apoA-I gene and familial hypoalphalipoproteinemia.

Familial hypoalphalipoproteinemia (hypoalpha), characterized by a decreased high density lipoprotein level, is associated with an increased incidence of premature cardiovascular disease. Restriction fragment length polymorphism analysis of genomic DNA has detected a polymorphism for the PstI restriction endonuclease near the apoA-I gene, with either a 2.2 or a 3.3 kb fragment. The latter has been previously found to occur with significantly higher frequency in probands of families with familial hypoalpha. ApoA-I was isolated from three unrelated subjects with familial hypoalpha and the 3.3 kb PstI polymorphism of the apoA-I gene, and from normal control subjects. The apoA-I from the hypoalpha subjects was structurally normal as determined by amino acid analysis and by two-dimensional gel electrophoresis. When normal apoA-I and hypoalpha apoA-I were simultaneously injected into either normal controls or hypoalpha subjects, both forms of apoA-I were catabolized at the same rate in the same subject, indicating that the hypoalpha apoA-I is also metabolically normal. Analysis of the kinetics of metabolism of apoA-I in the hypoalpha subjects, compared to the normal controls, revealed that the reduced plasma levels of apoA-I were due to an increased apoA-I fractional catabolic rate, and that the synthetic rate was normal. Based on these results, we conclude that the apoA-I gene in these hypoalpha subjects is normal, and the PstI polymorphism near the apoA-I gene, which is associated with familial hypoalpha, is likely to be a marker for a mutant gene closely linked to, but not in, the apoA-I gene.

Adult↗